1. Field of the Invention
The present invention relates to method of and apparatus for manufacturing an electrode assembly adapted for a battery having a rectangular structure, called “rectangular battery” hereinlater.
2. Related Art
An electrode assembly in a battery such as lithium ion secondary battery or cell is formed by alternately laminating positive electrodes and negative electrodes with a separator being disposed between a positive electrode and a negative electrode. Such electrode assembly may be manufactured by the following typical methods.
(1) Laminate Method: a separator, a positive electrode and a negative electrode, which are all formed in shape of sheet, are laminated such that the separator is disposed between the positive electrode and the negative electrode (for example, refer to the following Patent Document 5)
(2) Wind-up Method: a separator, a positive electrode and a negative electrode, which are all formed continuously, are wound up in form of eddy-shape such that the separator is disposed between the positive electrode and the negative electrode (for example, refer to the following Patent Documents 5, 6 and 7).
(3) Zigzag-Stack Method: a continuous member of a separator, or a laminated member of a continuous member of the separator and a continuous member of a negative electrode is folded in zigzag shape, and then, both sheet-shaped positive electrode and negative electrode or only a positive electrode is inserted into a valley groove of the laminated member, which is then crushed in flat shape (for example, refer to the following Patent Documents 1, 2, 3 and 4).
[Patent Document 1] Japanese Patent Laid-open Publication No. 2004-22449
[Patent Document 2] Japanese Patent Laid-open Publication No. HEI 1-122572
[Patent Document 3] Japanese Patent Laid-open Publication No. HEI 1-100871
[Patent Document 4] Japanese Patent Laid-open Publication No. 2006-190531
[Patent Document 5] Japanese Patent Laid-open Publication No. 2002-329530
[Patent Document 6] Japanese Patent Laid-open Publication No. 2000-223109
[Patent Document 7] Japanese Patent Laid-open Publication No. HEI 7-6783
In the laminate-method of the above (1), however, it is difficult to ensure the positional performance of the positive and negative electrodes and the separator, and in an adverse case in which their positions are shifted, the positive and negative electrodes may be short-circuited. When precise positional arrangement is made to prevent such short-circuiting, it may result in delay of takt time manufacturing speed per one electrode assembly), which may result in reduction of productivity of the electrode assembly, i.e., batteries.
In the wind-up method of the above (2), if the electrode assembly is wound up in too many turns, a space between the electrode assembly and a corner portion of a battery case may provide a dead space and electric capacity may be reduced, thus providing a problem.
The zigzag-stack method of the above (3) has merits such that in comparison with the above laminate-method, the positional performance between the positive and negative electrodes and the separator can be improved and the takt time can be reduced, and in addition, in comparison with the above wind-up method, the dead space can be reduced and the electric capacity can be increased.
In the conventional zigzag-stack method, for example, in the structure of the above Patent Document 1, however, a continuous separator is pinched by a pair of rollers and the paired rollers are reciprocated in the horizontal direction to thereby fold the separator in zigzag form and the positive and negative electrodes are alternately overlapped on the separator each time of the reciprocal motion of the paired rollers. This operation makes delay the takt time, which results in reduction of productivity, thus providing a problem.
Furthermore, in this zigzag-stack method, since it is intended to fold the separator in zigzag form on curved surfaces of the rollers, it is difficult to accurately fold the separator in the zigzag form and, hence, the separator, i.e., the electrode assembly, likely become warped, which may result in deterioration of performance of the battery. In addition, when the separator is folded in the zigzag form, the separator is moved in a meandering manner and, hence, is not accurately folded.
In the technology disclosed in the above Patent Document 2, it is intended to form the electrode assembly by clamping the continuous separator in the zigzag form between the hard positive electrode and negative electrode held with a constant interval, so that it may pose a problem such that the separator is likely broken by a large tension (load) applied to the separator, and in a case that the electrode is thin and soft, its manufacture is made difficult, thus also providing a problem.
In the structure disclosed in the above Patent Document 3, the zigzag-shaped separator is manufactured by placing the continuous separator on a saw-teeth shaped female mold half and sequentially inserting a male mold half having a shape corresponding to one groove into respective grooves. Next, the positive electrodes and the negative electrodes are respectively alternately inserted into the respective valley grooves of the separator, and finally, the separator is pressed together with the positive and negative electrodes to make the separator to provide a flat shape. In such method, the takt time is elongated and it is difficult to enhance the productivity.
In the structure disclosed in the above Patent Document 4, it is intended to manufacture the electrode assembly by pressing, in form of zigzag shape with a saw-teeth shaped male and female molds, a member in which the continuous separator is sandwiched between the continuous positive and negative electrodes and then pressing the thus formed zigzag-shaped laminated member. Therefore, in this manufacturing method, the zigzag-folding of the electrode assembly is made fine and the electric capacity is hence reduced, thus providing a problem. In addition, both the positive and negative electrodes are mutually contacted at certain positions, so that the positive electrodes and the negative electrodes may include portions not contributing to power generation, thus also providing a problem